Phototube multiplier



Afina, I uu UNITED STATES .PATENT oFFlcE Christian C. Larson, FortWayne. Ind., assignor, by menne assignments, to Farnsworth ResearchCorporation, a corporation o! Indiana application November-4, 1943,sulla No, tosses l This invention relates to electron-optical devicesand particularly` to a phototube multiplier for dividing an opticalimage into any desired pattern. l

In a conventional phototube multiplier for dividing an optical image thephotoelectric cathode is divided into the desired pattern. In thismanner a number of individual electron streams are emitted .by thecathode and each is separately multiplied by means of an individualelectron multiplier. In such a device the image division is securedbysubdividing the cathode in a desired manner. Such devices have notbeen entir'ely satisfactory for the reason that the formation o! asubdivided cathode is relatively dimcult. i

Another form of phototube multiplier comprises a. solid photoelectriccathode and one or more electron multipliers. Buch devices` however,have not been utilized for the division of an optical image according toa predetermined plan. The usual employment ot devices oi this characterhas been in modulation systems. The solid photoelectric cathode uponwhich light is projected serves merely to produce a copious stream oielectrons. Where a plurality or electron multipliers are used inconjunction with a a plurality of the image components.

Itis an object of the present invention, therefore. to provide a novelelectron-optical device',

whereby individual signals representative oi pre` determined portions ofan optical image may be produced.

Another object of the invention is to provide a novel method ofgenerating signals, whereby to produce simultaneously a plurality ofindividual signals each representative of a different pre-- determinedportion of an optical image.

In accordance with the invention there is provided an electron-opticaldevice having an evacuated envelope within which there is disposed aphotoelectric cathode. within the envelope a plurality oi electronmultipliers. Each of the multipliers is provided with asecondrryxniissive electrode oi predetermined There also is disposedSchmidt optical system.

s claim. (ci. aso-iis) 2 A form. These electrodes are disposed in a planspaced from and facing the cathode and arc arranged with respect to oneanother to form an area substantially similar to the area formed byprojecting the cathode surface into the plane of the electrodes.

Apparatus oi this character is one means for carrying out the novelmethod in accordance with the instant invention. This method oicontemporaneously producing individual signals representative oidifferent predetermined portions of an optical image comprises thefollowing steps:

An electron image corresponding to the optical image is formed. Adivision of the electron image into diiIerent predetermined portions iseffected. The different portions oi the elecline 2-2 of Fig. l.

Referring now to the drawing, there is disclosed an embodiment of theinvention employing an optical system of the reilection type which moreparticularly is known as the so-called This system comprises aspherically shaped light reflecting member il. There is formedsubstantially at the center thereof. an aperture i2. A concave surfaceI3 on the reflector Ii is conditioned by any well known means for thereection of light. A lens Il. having a conilguration suitable to correctfor spherical aberration ofthe r'eilector I I, is mounted in spacedrelation to the reilector by a plurality oi angular members such as thespacing members I5 and I8. Y Y

A substantially cylindrical transparent evacuated envelope Il issupported in a ,suitable manner so that it extends through the apertureI2 of the reilector II. Sealed through the lefthand end of the tubeenvelope I1, as viewed in the drawing, is a metallic rod I8. An opaque"metallic backing plate I8 is supported at the inner end of the rod I8and is provided with a substantially sphericalsuriace conilguration. A

photoelectric surface 2l is formed on the convex surface of the backingplate Il by any suitable process such as deposition by evaporation of aphotoelectric material. Such a structure constitutes a photoelectriccathode having a spherical surface facing and substantially parallel tothe reflecting surface I3 of the reflector Il. Preferably the cathode islocated approximately midway between the reflector Il and the lens Il.The photoelectric surface of the cathode is continuous over the entirearea thereof.

There is mounted in the righthand end of the tube envelope l1, as viewedln the drawing, four multistage electron multipliers. The ilrst stageelectrodes, such as 22 and 23l of the respective multipliers, areprovide with secondary emissive surfaces facing the photoelectriccathode 2i andare arranged in a plane a acen e reilector il. These firststage electrodes may have any predetermined forms depending upon the pattern into which it is desired to divide the optical,

image. For the purposes of illustrating the invention, it is assumedthat the optical image is to be divided into four equal quadrants.

Fig. 2 illustrates the arrangement of the electrodes 22 and 23 withrespect to one another and wi respect to the other two flrst stagemultiplier electrodes 2| and 25., It is seen that the first stagemultiplier electrodes are electrically dis` tinct and are arranged withrespect to one another to form an area which is substantially similar tothe projection of the photoelectric cathode 2i into the plane of theelectrodes.

The second stage multiplier electrodes. such as 26 and 21, associatedrespectively with the first stage electrodes 22 and 23, are so formed toprovide a guide path for the electrons from the cathode-facing surfacesof the ilrst stage electrodes to the rear or righthand sides oftheseelectrodes, as viewed in Fig. 1. The remainder of the electrodes of therespective multipliers may be the conventional box type structures, suchas 28 and 29. Each of the multipliers also is provided with a finalstage electrode which may be in the form of a plate, such as 3i or 32.Additionally. each of the multipliers is provided with a collectorelectrode which may be in the form of a grid structure, such as 33 or3l. Electrical connections to the various multiplier electrodes may bemade to the exterior of the tube envelope by means of conductors. suchas 35 and 36.

A coil 31 is mounted in a manner to surround the space between thephotoelectric cathode 2| and the multiplier flrst stage electrodes, suchas 22 and 23. Connections may be made from the coil to a suitable sourceof the direct current (not shown) by means of conductors 38.Energization of the coil produces a magnetic field which is employed tofocus the electron image produced by the photoelectric cathode 2|.

Referring now to the operation of the described embodiment of theinvention. assume that light forming the optical image, which it isdesired to divide into four equal quadrants, is directed from the leftas viewed in Fig. 1. This light is transmitted bythe lens i4 and isreflected by the reflecting surface i3 of the member Il., The reilectedlight is concentrated and directed onto the photoelectric cathode 2i.

The optical image projected onto the photoelectric cathode in the mannerdescribed, causes the cathode to produce a corresponding electronstream. The electron stream is focused by means of the coil 3l to forman electron image corresponding to the optical image in the plane of themultiplier first stage electrodes, such as 22 and 23. These electrodes,together with similar electrodes 24 and 25, are maintained, in a ywellknown manner, at suitable positive potentials with respect to thephotoelectric cathode 2i The electron image produced by the solidcathode is divided into four equal quadrants by the elec-l trodes 22,23, 24 and 25. This division of the electron image correspondssubstantially to the pattern of the multiplier first stage electrodearrangement.

Consider, for example. that portion of the electron image impinging uponthe secondary emissive surface of the rst stage electrode 22. Thesecondary electrons produced by the primary impingement are drawn intothe input aperture of the second stage electrode 23 by reason of themaintenance of the second stage electrode at a suitably higher positivepotential than the nrst stage electrode. The connections of themultiplier electrodes to a source of direct current potential have notbeen shown foi the reason that such connections are conventional tomaintain each succeeding multiplier electrode at an increasingly morepositive potential than its pred ecessor. The secondary electronstraversing the second stage electrode 26 emerge from the output aperturethereof and are directed sequentially through successive stages of themultiplier in a conventional manner.

The electrons collected by the collector electrode 33 are employed todevelop, in a conventional manner, the signal in an output impedance(not shown) connected to the collector electrode.

A similar process of electron multiplication is eiectedcontemporaneouslywith that described by the other electron multipliers. In each case theelectron multiplication is of that portion of the electron imagecorresponding in a pattern to the shape of the multiplier rst stageelectrode intercepting the electron image portion. Likewise, the signalsdeveloped in the respective output circuits connected to the individualmultiplier collector electrodes, are representative of the respectiveportions of the electron image. It is important to note that theindividual signal multiplications are effected simultaneously.

It is apparent from the foregoing description of the illustrativeembodiment of the invention. together with the described mode of itsoperation. that a device of this character is susceptible to employmentin numerous ways. Also .it is to be noted that it is not essential thatan electron-optical device of the character described be used inconjunction with an optical system of the reflection type. It iscontemplated to be `within the scope of the invention that a translucentphotoelectric cathode may be employed. In such a case. the optical imagemay be projected upon the surface of such a cathode opposite to thephotoelectric surface in a manner well known to those skilled in theart. lSimilarly, it should be noted that it is not essential to thesuccessful operation of a device embodying the invention that themultiplier be arranged in the manner shown. It is considered to bewithin the skill of those versed in the art to provide an arrangement ofa plurality of multistage electron multipliers in substantially anyother relationship to the photoelectric cathode so long as the ilrststage electrodes are disposed in a manner to intercept the electronstream produced by the cathode. Similarly, the configuration of thecathode may be substantially different from that shown so long as thearrangement of the multiplier rst stage electrodes forms an area winchis substantially similar to the projection of the cathode into the planeof the electrodes.

While there has been described what. at present, is considered thepreferred embodiment of the invention, it will be obvious to thoseskilled A in the art that various changesand modifications may be madetherein without departing from the invention. and it. therefore. isaimed in the appended claims to cover all such changes and modificationsas fall within'the true spirit cathode, each of said multipliers havinga secondary emissive electrode, said electrodes being disposed in aplane spaced from and facing said cathode and collectively havingsubstantially the same shape as the projection of said cathode into theplane of said electrodes.

2. In a phototube multiplier device, an evacuated envelope, aphotoelect,- ccathode disposed in said envelope, and a plurality ofelectron multipliers mounted in said envelope opposite to said cathode,each of said multipliers having a sector shaped secondary emissiveelectrode, said electrodes presenting together a substantially completecircular area in a plane spaced from and facing said cathode.

3. In a phototube multiplier device. a transparent evacuated envelope, aphotoelectric cathode disposed in said envelope, and' four electronmultipliers mounted in said envelope opposite to said cathode, each ofsaid multipliers having a quadrant shaped secondary emissive electrode.

said electrodes presenting together a substantially complete circulararea in a plane spaced from and facing said cathode.

4. A phototube multiplier device comprising, a reflecting member havingan aperture therein, a tube having a transparent evacuated envelopeextending through said aperture, a photoelectric cathode disposed insaid tube, the surface of said cathode facing and being substantiallyparallel to the surface of said reflecting member, a plurality ofelectron multipliers mounted in said tube opposite to said cathode, eachof said multipliers having a secondary emissive electrode. saidelectrodes being disposed in a plane adjacent to said reflecting memberand facing said cathode and presenting together an, area substantiallysimilar to the projection of said cathode into the plane of saidelectrodes, and means included with said device for producing a eld inthe space between said photoelectric cathode and s'aid multiplierelectrodes to focus the electron stream emitted by said cathodesubstantially in the plane of said electrodes.

disposed aperture therein, a tube having a transparent evacuatedenvelope extending through said aperture, a convex photoelectric cathodedisposed in one c nd of said tube, the surface of said cathode facingand being substantially parallel to the surface of said reflectingmember, a plurality of multistage electron multipliers mounted in saidtube opposite to said cathode, each of said multipliers having a flatfirst stage secondary emissive electrode, said first stage electrodespresenting together a substantially complete circular area in a planeadjacent to said reflecting member and facing said cathode. and meansincluded with said device for producing a field in the space betweensaid photoelectric cathode and said multiplier first stage electrodes tofocus the electron stream emitted by said cathode substantially in theplane of said first stage electrodes.

6. A phototube multiplier device comprising. a. concave reflectingmember having a centrally disposed aperture therein, a lens disposed inspaced relation to said reflecting member and having a configurationsuitable to correct for spherical aberration, a tube having atransparent evacuated envelope extending through said aperture. a convexphotoelectric cathode disposed in one end of said tube intermediate ofsaid reflecting member and said lens, the surface of said cathode facingand being substantially parallel to the surface of said reflectingmember, four electron multipliers mounted in said tube opposite to saidcathode, each of said multipliers having a quadrant-shaped secondaryemissive electrode, said electrodes presenting together a substantiallycomplete circular area in a plane adjacent to said reecting member andfacing said cathode, and electromagnetic means included with said deviceand located externally of said tube for producing a longitudinal fieldin the space between said photoelectric cathode and said multiplierquadrant-shaped electrodes to focus the electron stream emitted by saidcathode substantially in the plane of said electrodes.

7. A phototube multiplier device comprising, a spherically-shapedreflecting member having a centrally disposed aperture therein. a lensdisposed in spaced relation to said reflecting member and having aconfiguration suitable to correct for spherical aberration, a tubehaving a transparent evacuated envelope extending through said aperture,a spherically-shaped photoelectric cathode disposed in said tubeintermediate of said reflecting member and saidY lens, the surface ofsaid cathode facing and being substantially parallel to the surface ofsaid reflecting member, four multistage electron multipliers mounted insaid tube opposite to said cathode, each of said multipliers having arst stage quadrant-shaped secondary emissive electrode, said first stageelectrodes presenting together a substantially complete circular area ina plane adjacent to said reecting member and facing said'cathode, and anelectromagnetic coil included with said device and located coaxiallywith said tube for producing a longitudinal field in the space betweensaid photoelectric cathode 'and said multiplier first stage electrodesto focus the electron stream emitted by said cathode substantially intheplane of said first stage electrodes.

8. A vphctotube multiplier device comprising, a spherically-shapedreflecting member having a centrally disposed aperture therein, a lensdisposed in spaced relation to said reflecting member and having aconfiguration suitable to correct for 'spherical aberration, a tubehaving a transparent evacuated envelope extending through said aperture,a spherically-shaped photoelectric cathode disposed in one end of saidtube intermediate of said reflecting member and said lens, the surfaceof said cathode facing and being substantially parallel to the surfaceof said reflecting member, four multistage electron multipliers mountedin the other end of said tube opposite to said cathode, each of saidmultipliers having a first stage quadrant-shaped secondary 7 emissiveelectrode. said nrst stage electrodes being electrically distinct andpresenting together a substantially complete circular area in a planeadjacent to said reflecting member and facing said cathode, and anelectromanetic coil surrounding the space between said photoelectriccathode and said multiplier nrst stage electrodes to focus the electronstream emitted by said cathode substantially in the plane of said firststage electrodes.

CHRISTIAN C. LARBON.

REFERENCES CITED The following references are of record in the me oi'this patent:

5 UNITED STATES PATENTS Number Name Date 2,141,322 Thompson Dec. 27,1939 2,239,149 Farnsworth Apr. 22, 1941 2,204,428 Moller et a1 June 11,1940 1 2,192,579 Morton et a1 Mu. s, 1940- 2,230,134 Colberg et al. Jan.28, 1941

